Achieving ENERGY EFFICIENCY with Standard Air-Conditioning Units Mike West, PhD, PE Advantek Consulting, Inc
Standard Air Conditioning Unit Packaged Unit Split System DX (not chilled water) Air-cooled
ENERGY EFFICIENCY EER single point Energy Efficiency Ratio MBH per kw SEER (5 tons and less) Seasonal Energy Efficiency Ratio kbtu per kwh IPLV (10 tons and up) Seasonal Integrated Part-Load Value MBH per kw
FEMP Recommendation * *How to Buy an Energy-Efficient Commercial Unitary Air Conditioner NOVEMBER 2001
CEE Recommendation CEE's Tier I level is minimum industry standard. CEE's Tier II is the new "high efficiency" requirement, promoted by ENERGY STAR and FEMP. Minimum Allowable EER Ratings MBH per kw MBH 65-135 135-240 ASHRAE 90.1-1999 (Effective 10/29/2001) 10.3 9.7 CEE - Tier I 10.3 9.7 CEE - Tier II and EPA Energy Star 11.0 10.8 FEMP (as of 1/1/2002) 11.0 10.8 FEMP (after 1/3/2006) 12.0 12.0 MBH = kbtu/hr (1 ton = 12 MBH) (65 = 5.4 tons, 135 = 11.3 tons, 240 = 20 tons) CEE - Consortium for Energy Efficiency EER - Energy Efficiency Rating FEMP Federal Energy Management Program
Percent Meeting CEE Tier II* *http://www.cee1.org/resrc/updates/02-08hecac/02-08hecac.html
What is available today? Standard Efficiency IPLV 8.5 to 10.0 High Efficiency IPLV 9.5 to 14.0 So-called High Efficiency unitary products are 10% to 40% more energy efficient than Standard Efficiency. Systems 5-tons and smaller are as high as SEER 18 Water cooled-chiller systems are as high as IPLV 20
High Efficiency is really not very high is 20% to 60% LESS efficient than the best small split systems water cooled chiller systems they could be made (given a market) No Market No Products
Achieving ENERGY EFFICIENCY CAPACITY / SIZE SYSTEM DESIGN MODEL SELECTION INSTALLATION DUCTS OPERATION MAINTENANCE
CAPACITY / SIZE Avoid Over-sizing Frequent cycling shortens component life Efficiency ratings are at steady-state Costs more & uses more power Example: compare power draws of 2 units 15 ton: 15.7 kw 17½ ton: 18.9 kw Added electric demand of 3.2 kw ~ $300 per year Insist that documented sizing calculations be performed using accepted ACCA or ASHRAE procedures. ACCA methods have sufficient builtin safety factors. Use ASHRAE design conditions.
SYSTEM DESIGN Use manufacturer s performance tables to determine real unit capacity (not nominal rating) Select the model closest in capacity to the load Specify that TAB shall include supply air CFM, fan RPM, External SP, and EAT LAT OA CFM must meet ASHRAE 62, provide exhaust makeup, and pressurize the building 0.02 to 0.04 in.wg [5 to 10 Pa] Consider price to avoid value-un engineering
SYSTEM DESIGN Factory Equipment Options Filter pressure drop sensor Motorized fresh-air damper with Economizer Communications interface High Static Drive Use static regain duct design After-market Add-ons LPA liquid pressure amplification EER-Plus desuperheater / subcooler
MODEL SELECTION Efficiency Rating (IPLV, SEER, or EER) Fan motor efficiency rating Fan is 10 to 20% of unit power draw [kw] Fan is 20% to 50% of unit energy usage [kwh] Number of Stages Ease of Maintenance Price
MODEL SELECTION
MODEL SELECTION
MODEL SELECTION This unit has 2-compressors, but only 1 refrigerant circuit 1 2
MODEL SELECTION This unit has 4 compressors, but only 2 control stages 1 2 3 4
MODEL SELECTION Ease of Maintenance VS.
MODEL SELECTION Dual Source - the energy efficiency of ground-source with the low first cost of air-source Uses ground-coupling to extend the delta-t available from ambient air Application Example: MS Naval Training Classroom Building 24,730 square feet Two 35-ton Roof Top Package Units Electric Cost: STANDARD AC: $17,600 DUAL-SOURCE: $12,400 (30%) GEOTHERMAL: $8,000 (55%) Installed Cost / Payback STANDARD AC: $30,000 DUAL-SOURCE: $49,000 / 3.6 years GEOTHERMAL: $125,000 / 9.9 years
INSTALLATION Motorized Fresh-air damper with Economizer
INSTALLATION Operating EER can vary up or down by one point with the fan speed setting and proper matching of indoor and outdoor unit sections. Check these details to ensure the rated EER is realized.
DUCTS Air leakage and heat gain rob air-conditioning system efficiency. The insulation level of traditional ducting is typically only R-4 to R-6 (1.5 to 2.2 inches). Specify R-8 (3-inches) Leakage rates are typically 10% to 15% of total system airflow, sometimes higher. Specify ASHRAE Leakage Class-3 Test and Balance the Duct System
OPERATION Select a thermostat that will retain settings through a power outage, and that has a lockout or adjustment limits Program temperatures and occupied / unoccupied periods
MAINTENANCE critical to realizing rated EER for the life of the unit
MAINTENANCE Numerous energy surveys clearly show that lack of preventative maintenance is by far the major cause of air conditioning energy waste in FEDERAL buildings. Common and costly problems include: clogged, corroded cooling and condenser coils sizeable duct leaks and cabinet air leaks low refrigerant, even in brand-new units maladjusted air dampers un-calibrated or nonfunctioning thermostats
RECOMMENDED ACTION PLAN 1. Determine the actual operating efficiency of installed equipment. Compare with the best new equipment. 2. Identify units that are candidates for replacement if existing EER is 4 or more points less than the best new units. 3. Identify units that are candidates for upgrades existing EER is 2 to 4 points less than the best new units. 4. Identify units for a thorough preventative maintenance check and tune-up when the existing EER is within 2 points of the best available units.
Achieving ENERGY EFFICIENCY With Standard Air-Conditioning Units Thank you! Michael West, Ph.D., P.E. Building Systems Scientist Advantek Consulting, Inc. mwest@advantekinc.com